It is now well known that even small concentrations of long-chain polymers in a Newtonian solvent can give rise to interesting new behaviour [1]}. Perhaps the most extreme demonstration of this is the existence of `Elastic' turbulence (ET) at vanishingly small Reynolds numbers (\(Re\) ) where inertia is minimal [2]}, [3]}, [4]}. In 2013, a further multiscale, time-dependent state - `elasto-inertial' turbulence or EIT - was found which differs from Newtonian turbulence (NT) in being predominantly 2D and seems to require finite Reynolds number (\(Re=O(10^3)\) ) and Weissenberg number \(Wi=O(10)\)  to exist [5]}, [6]}, [7]}. Understanding exactly how these different types of turbulence relate to each other remains an outstanding challenge.
Work at the NT-EIT interface has so far focussed on the possible sustenance of elastically-modified Tollmein-Schlicting waves at least for very dilute solutions and weak elasticity [8]}, [9]}. Our focus here is the possible relationship between EIT and ET: are they two extremes of one whole [5]}, [11]}, [12]}, [4]} or distinct flow responses [14]} and figures 21 & 22 of [15]}?
Finding the dynamical origin for either could help in resolving this question.
